Synthesis of An Enantio-Enriched Iridolactone Core in Brasoside.

Abstract

A three step enantio-enriched protocol to the iridolactone core of brasoside is reported. Stereo-control reduction of [(1S,2R,3S)-3-methyl-2(nitromethyl)-5-oxocyclopentyl]acetic acid 3 afforded (3aR,4S,5R,6aS)-5-methyl-4-(nitromethyl)-hexahydrocyclopenta[b]furan-2-one 4. A further formylation strategy on the AB-ring system 4 afforded the enol ester 5, followed by Nef reaction of the nitoo functionality and acid quenching to the desired tricyclic lactone 11. Chiral ɤ-keto-acid 3 was used, since this precursor contains three functional groups: ketone, carboxylic acid, nitromethyl; it is also available in bulk as a pure enantiomer at low price